TELECOM Digest Thu, 30 Aug 90 19:27:00 CDT E-Series Recommendations
Inside This Issue: Moderator: Patrick A. Townson
E-Series Recommendations Excerpts [Joel M. Snyder]
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Date: Thu, 30 Aug 1990 01:13:43 MST
From:
Subject: E Series Recommendations Excerpts - for Edification and Emusement
Here are Interesting Facts and Figures entered from the CCITT
Recommendations of 1988. There are errata for these Recommendations,
but I have not applied them to these! Also, my typing skills are not
perfect.
Note: these are all excerpts, and quotes. I have left out substantial
text, and am including only some of the more interesting tidbits. If
you are really interested, make sure you get the entire text! Things
in [] are my comments.
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From Recommendation E.180, Technical Characteristics of Tones for the
Telephone Service
[I left out all the stuff about dB levels of tones, mostly because it was
accompanied by a lot of graphs]
Dial Tone: It is recommended that dial tone be either a single
frequency tone in the range 400 to 450 Hz, or a combined tone composed of
up to three frequencies, with at least one frequency in each of the ranges
340-425 Hz and 400-450 Hz. The difference between any two frequencies
should be at least 25 Hz.
When adopting a new single frequency dial tone, Administrations are
recommended to use 425 Hz.
Ringing Tone: Ringing tone is a slow period tone, in which the tone
period is shorter than the silent period. The recommended limits for
the tone period (including tolerances) are from 0.67 to 1.5 seconds.
The recommended limits for the silent period separating two tone
periods are 3 to 5 seconds. The first tone period should start as
soon as possible after the called subscriber's line has been found.
The ringing tone cadence should be similar to the cadence used for
applying ringing current to the called subscriber's telephone set, but
these two cadences need not be synchronized.
[It goes on to discuss frequencies for ringing tone]
Busy Tone and Congestion Tone: The subscriber busy tone and the
equipment or circuit group congestion tone are quick period tones in
which the tone period is theoretically equal to the silent period.
The total duration of a complete cycle (tone period E + silent period
S) should be between 300 and 1100 milliseconds.
The ration E/S of the tone period to the silent period should be
between .67 and 1.5.
The busy tone and the congestion tone can be identical, but a
distinction is desirable.
Special Information Tone: [This is that tri-tone we've been talking
about lately.] The special information tone has a tone period that
consists of three successive tone signals, each lasting for 330 +- 70
milliseconds. Between these tone signals may be a gap of up to 30
milliseconds. The frequencies used for the three tone signals are 950
Hz; 1400 Hz; 1800 Hz (all +-50 Hz) sent in that order. After the
special information tone is a 1000 millisecond (+-250 ms) silent
period.
[ Other tones are described: the warning tone to indicate that a
conversation is being recorded, the payphone recognition tone, the
call waiting tone (400 to 450 Hz for 300 to 500 ms, followed by 8 to
10 sec silence OR 400 to 450 Hz on for 100 to 200 ms, silent for 100
to 200 ms, and on for 100 to 200 ms, followed by 8 to 10 sec silence);
and caller waiting tone (you didn't know we had one of those, did you?
It's supposed to be similar to ringing, so if you don't know what it
is, it sounds like ringing)]
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Supplement 2 to Fascicle II.2 (E-series Recommendations)
This is a really interesting one. It gives the frequencies and
cadences for dial tones, ringing tones, busy tones, etc. around the
world. Example:
In Finland, the dial tone is a 425 Hz tone generated as three pulses
of .2 sec length separated by two pulses of .3 sec length, followed by
.8 second silence.
In El Salvador, the busy tone is 1/3 second tones of 425 Hz separated
by 1/3 seconds of silence.
In the US, the "special information tone" is three 1/3 second pulses
without pause at 950, 1400, and 1800 Hz.
God only knows how much of this is accurate, of course. I'm sure our
Finnish readers will be able to comment on the first.
-------------------
Recommendation E.123 Notation for National and International Telephone
Numbers
1.1 The international number should be printed below the national
number, with corresponding digits lined up one under the other to
facilitate understanding of the composition of the international
number as showd in the examples in 1.3 and 1.4 below.
1.2 The words "National" and "International" in the appropriate
langauge should be placed to the left of the national and
international numbers, and these should be separated by a horizontal
line.
1.3 Either the symbol for the telephone given in Rec. E.121 or the
word "Telephone" in the appropriate langauge should be placed to the
left of (or above) the national and international numbers (to avoid
confusion with other letterhead numbers.) The + (plus) signifies the
international prefix.
Example:
National (0607) 123 4567
Telephone --------------------------------------
International +22 607 123 4567
1.4 Because the countries of World Numbering >one 1 (North America)
have the country code 1, the same number as is used for the trunk
prefix, and because dialing between these countries is the same as
long-distance dialing within them, subscriber difficulties are avoided
by using an alternative notation that has been found superior for use
within those countries and equally good for subscribers in other
countries dialing to Zone 1.
Example:
Within N. Amer. zone (302) 123 4567
Telephone --------------------------------------
International +1 302 123 4567
1.5 If it is desirable to write only the international number, it
should be written in the form:
Telephone International +22 607 123 4567
1.6 [abbreviated: Extensions use the word "ext.", like this:]
National (0607) 123 4567
Telephone -------------------------------------- ext. 876
International +22 607 123 4567
2. Classes of symbols
[not too exciting, but there is one interesting part:]
4.4 Multiple numbers without automatic search
For a subscriber with multiple numbers who does not have automatic
search, the symbol / (oblique stroke, solidus, or slant) may be used
to separate the alternative numbers.
Example A: (0607) 123 4567 / 123 7272 / 627 1876
It is especially important that there be a space on either side of the
symbol /.
When it is desired to abbreviate the alternative numbers, and they are
consecutive, only the last digit should be shown for alternative
numbers:
Example B: (0607) 123 4567/8/9
It is especially important that there be no space on either side of
the symbol /.
4.6 Symbol to indicate the existence of an additional dial tone.
[Essentially: use a tilde (~), or as close as you can get to the
graphical representation of a full cycle of the sine wave. Don't use
a hyphen, and put spaces around it so it won't be confused for a
hyphen.
7. Facsimile number notation
The printed format for facsimile numbers should follow the conventions
set forth for voice telephone numbers except that facsimile numbers
should be clearly labeled with the upper case letters FAX printed to
the left of the numbers as illustrated here:
National (0607) 123 4567
FAX --------------------------------------
International +22 607 123 4567
--------------------------
E.163 and E.164 should be familiar to any of you ISDN hackers --
they're the numbering plan for the international telephone service,
which includes all of the Country Codes. Some of these have appeared
before in this forum. I won't retype them.
---------------------------
E.161 Arrangement of Figures, Letters, and Symbols on telephones and
other devices that can be used for gaining access to a telephone
network:
1. Use of figures and letters in telephone numbers
[Don't use figures. Use numbers]
2. Rotary dials.
[There's a picture there, which looks like our standard rotary dial,
sort of. The holes are numbered from 1 to 0, with the letters as
follows:
1 (none)
2 ABC
3 DEF
4 GHI
5 JKL
6 MN
7 PRS
8 TUV
9 WXY
0 OQ
]
3. Pushbuttons or keys
3.1 10 buttons
[More figures. Essentially says:
1 2 3
4 5 6
7 8 9
0
Also, if you HAVE to, you can do:
1 2 3 4 5
6 7 8 9 0
or
1 2
3 4
5 6
7 8
9 0
with a note: "User dialing performance on these special arrays is
slightly inferior to that on the standard array given above."]
The letters are the same as on rotary dials; note the letter O is on
the number 0, and not on the number 6.
3.2 12 buttons
[Add * and # in the usual places. There's this big picture of the *,
and it will be known as the "star."
Also, there's two big pictures of the #, which I'll try to reproduce
here:
X X
X X
XXXXXXXXXXXXXXXXXXXXX
X X
X X
X X
X X
X X
X X
XXXXXXXXXXXXXXXXXXXXX
X X
X X
The length of the long bar is b, and the length of the stub after the
cross (two Xs in my picture) is called a. The angle is called alpha.
In Europe,
alpha = 90 degrees with a/b = 0.08
In North America,
alpha = 80 degrees with a/b close to the upper limit of 0.18
This symbol will be known as the square.
[There's more, noting that you shouldn't color the pushbuttons
different colors, and you should have a register recall pushbutton
instead of using switchhook flash.]
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Recommendation E.114 Supply of Lists of Subscribers
1. Each Administration shall supply by mutual agreement and free of
charge to the Administrations with which a telephone service exists a
sufficient number of copies of its lists of subscribers for official
use.
2. A subscriber wishing to obtain a telephone directory of another
country must apply to his own Administration. If an application for
one of its telephone directories is received directly by an
Administration by a subscriber in a foreign country, the receiving
Administration shall inform the subscriber that such requests should
be addressed to his own Administration.
3. An Administration which has supplied telephone directories of its
own country to another Administration for distribution to subscribers
shall indicate the sale price of the directories plus any postal
charges (in principle expressed in gold francs) for the use of the
receiving Administration.
4. Accounting concerning the supply of such directories for
subscribers' use shall be conducted according to the usual procedure
followed between Administrations (see Recommendation D.170) unless
Administrations, by mutual agreement, elect to forego such accounting.
[typed in its entirety]
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Recommendation T.20, Standardized Test Chart for Facsimile Transmissions
You probably have heard of this test chart, since that's what your FAX
manufacturer used to propose the incredibly high rate of transmission
you never see on your own equipment. The funny part of this one is
that the test chart has some half tones, some lines, and other stuff,
but the center is a picture of a small child: "Argentine Boy." One
wonders how long they had to argue over the picture...
T.21 is a second test chart, which has texts in English, French,
Spanish, Chinese, Arabic, and Russion.
-------------------------
Recommendation E.117 Provisions concerning the device substituting a
subscriber in his absence
1. Precautions will have to be taken by the Administrations to warn
callers of the presence on the called subscriber's line of a device
substituting him in his absence:
a. Devices of this type should be indicated in the telephone
directories by means of a special sign [...]
[Here, I'll try to describe the sign. It looks very much like a
backwards Q: There is a large circle, larger than any other character
in the type face, with a small stroke through it, going South-West.
The stroke doesn't go quite to the center, and extends out about as
far as it extends in. I bet the angle is exactly 45 degrees (or 225,
if you want to think of it that way).]
b. Administrations should invite the owners or renters of such
equipment to mention the fact on their letterheads by means of a
printed indication.
2. To facilitate the disposal of international traffic on a device of
this type, the Administrations should, when consenting to this
equipment, insist that it complies with the essential conditions set
out in the following Annex.
(end of Recommendation, beginning of Annex A to Recommendation E.117
A.1 Operating Conditions
A.1.1 Delay in Answering
The ringing current from the telephone exchange should be premitted to
operate the telephone bell for at least three seconds but not for more
than ten seconds before the call is answered by the apparatus. This
will enable the call to be answered in the normal way in those
countries which wish to provide for such a facility. The timing of
this interval (three to ten seconds) should be independent of the
periodicity or the duration of the ringing current.
A.1.2 Normal conditions for metering and supervision
In answering a call the apparatus should loop the subscriber's line
and should give the normal conditions for control of metering and for
supervision as with a normal subscriber's installation. The
disconnection of the apparatus should break the loop on the
subscriber's line.
A.1.3 Announcement of the presence of the apparatus
A.1.3.1 The presence of the apparatus should be indicated to the
calling party by means of a verbal announcement following, in
principle, immediately on the closing of the loop on the subscriber's
line.
A.1.3.2 This verbal announcement should include, in particular, the
following:
- first, that it is a reconding apparatus;
- the subscriber's name or business style;
- the subscriber's number and particulars of the locality (e.g.,
Geneva, St. Moritz, etc.)
- clear instructions as to the functioning of the apparatus
(whether a message may be recorded, and if so, the moment
when the message may be recorded and the maximum duration
of the recording).
A.2 Signalling conditions
A.2.1 Avoidance of interference from signalling frequencies
The correct functioning of the apparatus should not depend upon (nor
be affected to any extent by) the sending or receiving of signalling
frequencies used in the telephone system or specially generated in the
apparatus.
A.2.2. Avoidance of interference with national signalling systems by
the tones transmitted by the apparatus
To avoid interference with the national signalling system of a country
by the tones transmitted by the apparatus over the network of that
country, it is recommended that:
- the transmission of tones should be in short pulses and not a
continuous transmission;
- the tones should not be composed of a single frequency, but
should be a mixture of at least two frequencies, so that
the guard circuit of the signal receiver of the
corresponding country, where there would be a risk of
interference, may operate. For this purpose, the choice
of the following frequency-combinations should be avoided:
2040 and 2400 Hz
600 and 750 Hz
1200 and 1600 Hz
500 and 20 Hz
1000 and 20 Hz
A.3 Transmission Conditions
Any recording apparatus which takes the place of the called subscriber
should give a level and quality of speech comparable to that given
when the station is used by a person.
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End of TELECOM Digest Special: E-Series Recommendations
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